﻿using System;
using System.Collections.Generic;
using System.Text;

namespace NAudio.Codecs
{
    /// <summary>
    /// a-law decoder
    /// based on code from:
    /// http://hazelware.luggle.com/tutorials/mulawcompression.html
    /// </summary>
    public class ALawDecoder
    {
        /// <summary>
        /// only 512 bytes required, so just use a lookup
        /// </summary>
        private static readonly short[] ALawDecompressTable = new short[256]
        {
             -5504, -5248, -6016, -5760, -4480, -4224, -4992, -4736,
             -7552, -7296, -8064, -7808, -6528, -6272, -7040, -6784,
             -2752, -2624, -3008, -2880, -2240, -2112, -2496, -2368,
             -3776, -3648, -4032, -3904, -3264, -3136, -3520, -3392,
             -22016,-20992,-24064,-23040,-17920,-16896,-19968,-18944,
             -30208,-29184,-32256,-31232,-26112,-25088,-28160,-27136,
             -11008,-10496,-12032,-11520,-8960, -8448, -9984, -9472,
             -15104,-14592,-16128,-15616,-13056,-12544,-14080,-13568,
             -344,  -328,  -376,  -360,  -280,  -264,  -312,  -296,
             -472,  -456,  -504,  -488,  -408,  -392,  -440,  -424,
             -88,   -72,   -120,  -104,  -24,   -8,    -56,   -40,
             -216,  -200,  -248,  -232,  -152,  -136,  -184,  -168,
             -1376, -1312, -1504, -1440, -1120, -1056, -1248, -1184,
             -1888, -1824, -2016, -1952, -1632, -1568, -1760, -1696,
             -688,  -656,  -752,  -720,  -560,  -528,  -624,  -592,
             -944,  -912,  -1008, -976,  -816,  -784,  -880,  -848,
              5504,  5248,  6016,  5760,  4480,  4224,  4992,  4736,
              7552,  7296,  8064,  7808,  6528,  6272,  7040,  6784,
              2752,  2624,  3008,  2880,  2240,  2112,  2496,  2368,
              3776,  3648,  4032,  3904,  3264,  3136,  3520,  3392,
              22016, 20992, 24064, 23040, 17920, 16896, 19968, 18944,
              30208, 29184, 32256, 31232, 26112, 25088, 28160, 27136,
              11008, 10496, 12032, 11520, 8960,  8448,  9984,  9472,
              15104, 14592, 16128, 15616, 13056, 12544, 14080, 13568,
              344,   328,   376,   360,   280,   264,   312,   296,
              472,   456,   504,   488,   408,   392,   440,   424,
              88,    72,   120,   104,    24,     8,    56,    40,
              216,   200,   248,   232,   152,   136,   184,   168,
              1376,  1312,  1504,  1440,  1120,  1056,  1248,  1184,
              1888,  1824,  2016,  1952,  1632,  1568,  1760,  1696,
              688,   656,   752,   720,   560,   528,   624,   592,
              944,   912,  1008,   976,   816,   784,   880,   848
        };

        /// <summary>
        /// Converts an a-law encoded byte to a 16 bit linear sample
        /// </summary>
        /// <param name="aLaw">a-law encoded byte</param>
        /// <returns>Linear sample</returns>
        public static short ALawToLinearSample(byte aLaw)
        {
            return ALawDecompressTable[aLaw];
        }
    }
}
